It is already known that numerous isothiazolecarboxylic acid derivatives have fungicidal properties (of U.S. Pat. No. 5,240,951 and JP-A 06-009 313). Thus, for example, N-furfuryl-3,4-dichloro-isothiazole-5-carboxamide and N-morpholinyl-3,4-dichloro-isothiazole-5-carboxamide can be employed for controlling fungi. The activity of these compounds is good, but in some cases leaves something to be desired at low application rates.